The Pelvis and Structural Adaptions to Pregnancy

Question 1

What are the anatomical boundaries of the perineum?

Answer 1

• Anteriorly, pubic symphisis
• Anterolaterally: ischiopubic ramus
• Laterally: ischial tuberosity and sacrotuberous ligament
• Posteriorly: coccyx

Question 2

We’re looking down into a Kenhub image of pelvic floor muscles. What muscles do we see?

Answer 2

• Levator ani (pubococcygeus, puborectalis, iliococcygeus)
• Ischiococcygeus (sometimes called coccygeus)
• Piriformis posterolaterally
• Obturator internus anteriorly

Question 3

Describe the perineal muscles (including those that relate to the genitals)

Answer 3

• Superficial/deep transverse perinei
• Pair of ischiocavernosus
• Bulbospongiosus

Question 4

What is the primary nerve supplying the pelvic floor and perineum? Is it autonomic/motor/sensory?

Answer 4

• Pudendal nerve
• It is motor, sensory, and autonomic

Question 5

Urogenital vs pelvic diaphragm

Answer 5

• Pelvic diaphragm forms the floor for all pelvic organs
• Urogenital diaphragm is outside this, and supports the urethra and surrounding structures anteriorly

Question 6

Structure of male vs female pelvis

Answer 6

• Female pelvis has thinner, lighter bones (why?)
• Women have larger pelvic inlet/outlet (why?)
• Women have wider subpubic angle (why? :))
• Women have wider, shorter sacrum with outward/down curving coccyx

Question 7

Which veins/arteries drain/supply the pelvis? Which specific branch of these drain/supply the perineum?

Answer 7

• Pelvis is supplied by internal iliac v/a
• Pudendal v/a supply the perineum (primarily internal pudendal)

Question 8

What changes occur to the pelvis/surrounding muscles during pregnancy? What hormone(s) mediate this?

Answer 8

• Relaxin and oestrogen soften the joints and connective tissue (incl. ligaments)
• Pubic symphysis widens
• Pelvic floor muscles soften